bnc#580834: HTML import: Embed images if source URL is a local file.

Use also INET_PROT_FILE to determine whether to import images as links.

Change-Id: I072be21086505f6300463e4e3cfb276cbe506803
sw: html import test: local images shouldn't be file links (bnc#580834)

Change-Id: Id35e03a3f814609e40e4beea778e66cce39054d1
bnc#591147: unit test for media files import

Change-Id: Ie45818c54d756628e9cbc2619e5ad43cedcac92c